Screws are used to fix one object to another one. The design of the screw is based on the materials and characteristics of the materials.
However, in screwing, material features of the screw, such as hardness, density and textures of the materials, will induce the problems such that in drilling, the dregs from drilling left on outer side of the wall of the object to be drilled so as to deteriorate the appearance of the object to be drilled. To improve such problem, ribs, such as block-form ribs, linear ribs, arc ribs, sharp ribs and others, are developed to prevent the problem of the dregs on the outer side of the object to be drilled. However, all the prior arts are not perfect.